As known, a laser source has a narrower emission spectrum than a LED source. The use of the laser source in a projection apparatus is able to result in better color purity and create vivid images with extensive color coverage. With increasing development of the information generation, laser projection apparatuses with the portable and easy-to-use benefits are widely used in conferences, offices, schools and homes. For example, a pico projector is one of the most popular laser scanning projection apparatuses.
Due to the above advantages and benefits, laser projection apparatuses are gradually adopted. However, if the user is exposed to the surroundings of a laser projection apparatus for a long time, the laser radiation energy may cause injury to the user. For example, the exposure of the laser beam may hurt the user's eyes or skin. For protecting the user from the risk of the laser beam, the safety regulations of the laser products in the world become stringent increasingly. For example, the national standard IEC-60825-1 is the safety standard of laser products emitting laser radiation. According to the safety regulations, the exposure radiation energy of the laser products in the normal condition and the single fault condition should be lower than the accessible emission limit.
FIG. 1 schematically illustrates the architecture of a conventional laser projection apparatus in a normal working mode. As shown in FIG. 1, the conventional laser projection apparatus 1 comprises a laser diode driver (LDD) 11, a laser diode (LD) 12, a reflective mirror 13, a scanning mirror 14, an optical sensor 15, and a controlling unit 16. These components are accommodated within a casing 10. The laser diode driver 11 is configured to issue a driving signal Sd. In response to the driving signal Sd, the laser diode 12 is driven to emit a laser beam 121. When the laser beam 121 is reflected by the reflective mirror 13, the laser beam 121 is directed to the scanning mirror 14. For example, the scanning mirror 14 is a two-dimensional microelectromechanical (MEMS) scanning mirror.
When the laser beam 121 is reflected by the scanning mirror 14, the laser beam 121 is transmitted through a light-outputting port 101 of the casing 10 to be projected on a projection surface (not shown) according to a raster scanning trajectory or a Lissajous scanning trajectory. Moreover, the optical sensor 15 is used for detecting the laser beam 121 which is reflected by the reflective mirror 13, and outputting a corresponding sensing signal S1 to the controlling unit 16. According to the difference between the sensing signal S1 and a predetermined laser signal S0, the controlling unit 16 issues a control signal Sc to the laser diode driver 11. According to the control signal Sc, the laser beam 121 is correspondingly adjusted and compensated.
In practice, for simulating the single fault condition, the laser diode driver 11 is connected to a ground terminal to disable the laser diode driver 11. Under this circumstance, the laser beam 121 from the laser diode 12 has the maximum power. For protecting the user's eyes or skin from injury of the strong laser beam 121, the laser projection apparatus 1 should have a special safety device or take a special protection measure such as a remote controlling mechanism or an interlocking mechanism.
Therefore, there is a need of providing a safety protection method for a laser projection apparatus. By using the safety protection method, the laser projection apparatus can pass the single fault test of the laser product.